I know that. But I wonder how an electrical field will change the results, experimentally.

I thought it could be done, maybe with different nanomaterials ordered in grids, lines and layers. The charges must be confined somehow.

I search a "proof" that there is an attractive force and a repulsive force, not only a repulsive one. This is a challenge to the equivalence principle. Not that I think this principle is totally wrong but it could be modified. Why inertia is local and gravity is not?

Don't rely on the equivalence principle to prove the equivalence principle...